IGHM and idiopathic pulmonary fibrosis: Between the mild and severe IPF cohort , and between normal and severe disease, there is up-regulation of several other host defense genes including defensin A4 (DEFA4), cathelicidin antimicrobial peptide (CAMP), cathespin G (CTSG), and down-regulation of immunoglobulin heavy chain constant mu (IGHM).